The present invention relates to an engine unit for vehicles.
Most present-day motor vehicles with four or two wheels are propelled by a thermal engine which utilizes the expansion of a fuel/oxidant mixture in order to drive in rotation an output shaft, the movement of which is transmitted to the wheels of the vehicle by means of gear and step-down devices.
The starting of this thermal engine is ensured by an electrical starter fed by a battery. During starting, the battery supplies current to the motor of the starter which, by means of a reducer and a suitable interlock system ("Bendix"), drives the crown of an inertia disc or flywheel fixed to the drive shaft. As soon as the thermal engine is started, the Bendix uncouples the starter motor from the inertia disc, and the drive of the shaft is ensured by the thermal engine alone.
Moreover, the thermal engine drives an alternator by means of a gear device which conventionally comprises pulleys and belts. By means of an electronic regulating device, this alternator supplies an electrical current which makes it possible to recharge the battery.
The sets of electromechanical connections between the battery and the thermal engine which were mentioned above are relatively complex and are an appreciable source of breakdowns.
Furthermore, their use is limited to the above-described functions of starting and of recharging the battery.
U.S. Pat. No. 4,148,192 makes known an engine unit for a vehicle, comprising a thermal engine and an electric motor, such that it can operate without being disconnected mechanically from the thermal engine when the latter rotates at its operating speed.
However, such an engine unit is limited to a thermal engine of low power, itself alone insufficient for ensuring the acceleration of the vehicle. It is only sufficient for maintaining the latter at a reasonable cruising speed.
Advances in electrical engineering and electronics make it possible to rethink the problem completely in order to achieve the greatest possible embodiment simplicity.
The articles "VW GOLF with a compact single shaft Diesel-Electric hybrid propulsion system", by R. MIERSCH, S. SCHUSTEK and R. WIRTZ (INGENIEURS DE L'AUTOMOBILE, June 1987, pages 112-118) and the corresponding German version "VW GOLF mit kompaktem Einwellen-Diesel Elektro-Hybridantrieb", disclose an engine unit for a vehicle comprising a thermal engine and a coaxial relatively flat electric motor which can operate up to, at least, the maximum operating speed of said thermal engine, and which has a rotor and a stator both having a structure made of magnetic material and at least one of them having electrical windings, the rotor having a diameter substantially similar to the diameter of a flywheel normally associated with said thermal engine and an axial length several times smaller than said diameter but not substantially smaller than the axial length of said flywheel, and being constructed and arranged to have an inertia sufficient to perform the speed stabilizing function of said flywheel and replacing said flywheel, said electric motor being associated with controls providing energy to said electric motor and allowing said electric motor to operate also as a generator.
The Diesel engine, a 1.6 liter Diesel engine, has a joint drive shaft with a 6KW, 3-phase asynchron electric motor.
The Diesel engine has a maximum power of 40 KW and a maximum torque of 100 Nm.
The electric motor has a base speed area of 6-2,800 RPM, a maximum speed of 6,000 RPM, a shaft output of 6 KW, a torque in the base speed of 21 Nm, a weight of 8.5 kg, a stator outside diameter of 0.3 m, a total axial length of 0.068 m, a length of magnetic sheet stack of 0.028 m.
The rotor is a squirrel cage rotor. The electric motor has 6 pairs of poles, and the motor current is controlled to the required amplitude and frequency by a single current transducer.
A clutch is provided between the Diesel engine and the electric motor, and a second clutch is provided between the electric motor and a conventional gearbox.
For starting the Diesel engine, the two clutches are declutched, the electric motor is started and rotated until it attains a starting speed which may vary between 825 RPM and 1300 RPM depending on the temperature of the engine. Then, the clutch between electric motor and Diesel engine is activated and the Diesel engine is cranked to start by the kinetic energy of the electric motor. This process is the same for a gasoline engine having a maximum torque of 123 Nm.
Such a starting procedure is not acceptable for a conventional vehicle.
Thus, the object of the present invention is to provide an original association of a thermal engine and of an electric motor, in order to simplify these electromechanical devices, whilst at the same time making it possible for them to perform additional functions.